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Re: Setting arbitrary tire sizes for speedometer calibration

Posted: Fri Oct 12, 2018 5:43 pm
by becausebear
Can anyone confirm or deny that this method would work on an '11 escape? I've compared ABD with another escape with different stock tires and have found one bcm line change and four abs line changes, but not sure as to which one to alter.

using the excel calulator at the start of this thread results in a 225/65/17 showing as xxxx 0898 xxxx which i do not see in the bcm or abs lines

what i have found, in the pcm log in forscan, is that it has a listing of tire sizes and corresponding rpm. it shows my stock 225/65/17 as 731, which is off, as its 708 rpm. but factoring in a 98.65% conversion gets me 731 rpm.

Wonder if i could find a way to alter the pcm's tire rpm value.

Solved my own issue, for anyone who was curious this vehicle has it in the pcm, forscan is unable to change it beyond factory settings. Ended up using an sct tuner to adjust it.

Re: Setting arbitrary tire sizes for speedometer calibration

Posted: Wed Nov 07, 2018 6:49 am
by ggandzz
hi, I have a few questions to ask you. If you only change the tire size, can the relevant ABS or other safety aids work properly? For example, Mustang 2015-2.3T-255-40-19, according to your formula, the original value is 208 5, that is 0825. If I change to 275-35-20, will it become 2128, that is 0850? Is the power conversion factor calculated according to 96.7% or else? Please give me a hand.

Re: Setting arbitrary tire sizes for speedometer calibration

Posted: Sat Dec 01, 2018 6:10 am
by Aussiejoe
Does anyone know if it's possible to change tyre size on a 2008 transit van fwd 2.2? Thanks

Re: Setting arbitrary tire sizes for speedometer calibration

Posted: Tue Jan 15, 2019 10:33 pm
by dcag14@verizon.net
I have a 2015 Ford Fusion Titanium. Ever since I bought it there has been a 2 mph speedometer error compared to GPS - at 70 mph on GPS, speedometer reads 68. Used the spreadsheet calculator found elsewhere on this forum to change BCM 726-12-01 from xxx-0804-xx to xxx-07CB-xx. Test drove right away. Amazing! Speedometer exactly matches GPS now.

Tire size is 235-45-18. Stock for Titanium trim.

Re: Setting arbitrary tire sizes for speedometer calibration

Posted: Wed Jan 16, 2019 9:21 pm
by jeff6146
DCAG14, that's pretty normal to only be off 2MPH. That's why we wont issue tickets for that unless you run across an a**hole having a bad day. But it is his/her discretion as to when or when not to issue a ticket. most of the time they pull you over to just inform you so you are aware. but to answer your question, someone posted a formula to get it down to the money. someone else had a good idea and that's to check it after using GPS, or just let a cop tag you with a radar.

Re: Setting arbitrary tire sizes for speedometer calibration

Posted: Mon Jan 28, 2019 1:21 pm
by jeff6146
Here is my problem, when I try to reset the tire size and perform the function none of the tire size configuration’s in the module will work. So I can’t get past even riding the module for the tires as I have. Has anyone else put 35x12.50x17’s on their 2015 F350 Dually? Mine is a Lariat FX4 which I’ve upgraded to the sync3.

This is what should have worded
Toyo Open Country MT 35x12.5x18 726-12-01 xxxx 0A50 xxxx

So I then tried everyone of these and none would work.

BFG KO2 35x12.5x20 726-12-01 xxxx 0A7F xxxx Freeseframe
Nitto Ridge Grapplers 35x12.5x20 726-12-01 xxxx 0A57 xxxx dominatorlp
Toyo Open Country A/T 35x12.5x20 726-12-01 xxxx 0A8F xxxx Kaye Kolb Jr.
Toyo Open Country MT 35x12.5x18 726-12-01 xxxx 0A50 xxxx Timc74
Nitto Ridge Grapplers 35x11.5x20 726-12-01 xxxx 0A3D xxxx gonethinkn
BFG KO2 34x10.5x17 726-12-01 xxxx 09FF xxxx 17x7 (Dually) ZooDad
BFG KO2 315/70/R17 726-12-01 xxxx 0A68 xxxx robbieg
BFG KO2 305/65/18 726-12-01 xxxx 0A21 xxxx DeltaNu1142
BFG KO2 285/70/17 726-12-01 xxxx 09E7 xxxx jpeckinp
Cooper AT3 275/70R18 726-12-01 xxxx 09E7 xxxx Scott91370
Falken Wildpeak A/T3W 275/70R18 726-12-01 xxxx 09E7 xxxx waphilips
Michelin LTX A/T2 275/65/20 726-12-01 xxxx 0A45 xxxx TX-FJuan50

Re: Setting arbitrary tire sizes for speedometer calibration

Posted: Mon Jan 28, 2019 8:20 pm
by Andyfocus
have you tried resetting to as built and do it then change the sync because you have changed the unit ?.
at least then you can use the original tyre size setting and leave it alone till a solution is found ?

Re: Setting arbitrary tire sizes for speedometer calibration

Posted: Mon Jan 28, 2019 10:48 pm
by jeff6146
the tire size is at the as built. its the same numbers.

Re: Setting arbitrary tire sizes for speedometer calibration

Posted: Mon Jan 28, 2019 10:52 pm
by jeff6146
Perhaps run the force adapt learn the codes in it so it thinks nothing has changed? I seen someone talking about how to make the ecm learn the new stuff and forget the old stuff. not sure where I seen it, id have to find that. maybe someone on here can lend a hand if they have it saved.

Re: Setting arbitrary tire sizes for speedometer calibration

Posted: Tue Feb 26, 2019 1:48 am
by BOSSC351
275 65 20 Radar Renegade LT tire on a 2013 F-150. Spreadsheet shows 0A45. I input this and I am 6 MPH off. Speedo shows 70 and I am traveling at 76 per the GPS. I have tried the GPS calculation and still off by about the same. What in the world am I doing wrong?